A direct correlation has been established between stacking faults in a -plane GaN epilayers and luminescence peaks in the 3.29-3.41 eV range. The structural features of the stacking faults were determined by diffraction-contrast transmission electron microscopy, while the optical emission characteristics were observed by highly spatially resolved monochromatic cathodoluminescence. The studies were performed in the exact same regions of thinned foils. We find that stacking faults on the basal plane are responsible for the strong emission at ~3.14 eV. Luminescence peaks at ~3.33 and ~3.29 eV are associated with the presence of stacking faults on prismatic a planes and partial dislocations at the stacking fault boundaries, respectively. © 2005 American Institute of Physics.